Potassium bearing aqueous solutions, viz., sea bittern left after recovery of common salt in solar salt work is a rich source of the element (20-25 g/lit potassium chloride). Similarly, the natural bittern of Greater Rann of Kutchh (Gujarat, India) is a perennial source of potassium. Evaporite based technologies rely on solar evaporation of bittern and require large amount of land area apart from favourable climatic conditions for consistent production of the potassic feedstock.
Reference may be made to U.S. Pat. No. 7,041,268, May 9, 2006 by Ghosh P. K. et al. which teaches about an integrated process for the recovery of sulphate of potash (SOP) from sulphate rich bittern. However, this process depends on evaporation of intermediate streams for production of potassium chloride, required in the process. This creates additional demand for large amount of land area apart from need effective integration of plant & field operations.
Selective extraction of potassium offers a practical & implementable alternative to overcome the afore-mentioned impediments faced by evaporite based technologies.
Reference may be made to U.S. Pat. No. 2,617,710, Nov. 11, 1952 by Kielland J. et al. which teaches an efficient method for extraction of potassium from dilute solution, e.g., sea water, using dipicryl amine as extractant. However, commercial implementation of the process poses serious operational & environmental issues owing to hazardous nature of dipicryl amine.
Reference may be made to U.S. Pat. No. 8,182,784, May 22, 2012 by Paul P. et al. which teaches an efficient method for extraction of potassium from SEL, the potassium rich intermediate stream generated upon decomposition of kainite type mixed salt, as described in U.S. Pat. No. 7,041,268, in the form of potassium chloride, using dipicryl amine as extractant. However, in this instance also, commercial implementation of the process poses serious operational & environmental issues owing to hazardous nature of dipicryl amine.
Thus a need was felt to devise a process to selectively extract potassium from bittern & other K bearing aqueous solutions for production of potassic fertiliser using a recyclable, benign & environmentally safe extractant.
It was quite well known that potassium bitartrate (cream of tartar) has substantially lower solubility than sodium bitartrate. Cream of tartar, a derivative of wine industry attracted lot of attention, particularly in regard to recovery of tartaric acid & potassium salts.
Reference may be made to U.S. Pat. No. 957,295, May 10, 1910 by Alberti A. et al. which teaches about process of recovering potash salts from wine lye (raw cream of tartar).
Reference may be made to U.S. Pat. No. 2,710,789, Jun. 14, 1955 by Boeri G. et al. which teaches about method for preparing substantially pure potassium nitrate from raw tartaric materials.
Reference may be made to U.S. Pat. No. 3,069,230, Dec. 18, 1962 by Pescarolo B. et al. which teaches about process for extracting Tartaric Acid and Potassium in form pure potassium nitrate in the cold from tartaric acid, without the need of previous roasting of the tartaric raw material.
The above mentioned inventions used wine lees (raw cream of tartar—crude potassium bitartrate) as the potash bearing raw material. Moreover, the aforesaid patents do not teach us about recycling of the extractant, i.e., tartaric acid.
Reference may be made to the paper “Adaptation of the bitartrate method for the estimation of potassium in sea bittern” by Shukla, B. K. et. al (http://www.csircentral.net/index.php/record/view/88029) which teaches about the method for estimation of potassium content of bittern, by precipitating potassium as potassium bitartrate. Although developed as a method for analysis, the main disadvantages for practicing this process are that it requires addition of methanol/ethanol, & sodium hydrogen tartrate apart from tartaric acid for precipitation of potassium bitartrate.